Subminiature electric lamp having a composite envelope

ABSTRACT

The lamp, which may be of the incandescent or photoflash-type, has an envelope composed of segments of light-transmitting and infrared-radiation absorbing glass tubing that are sealed together in abutting relationship. The infrared-radiation absorbing end portion of the composite envelope is hermetically sealed to the lead wires and the seal is formed by focusing a beam of infrared radiation on the seal assembly. The envelope is evacuated, and filled with gas if desired, through its opposite end which is then tipped off. Oxidation of the lead wires is reduced to a minimum by forming the seal inside a chamber that is evacuated, or filled with an inert gas, and has walls which transmit infrared radiation. In the case of chamber sealing, the free end of the light-transmitting portion of the envelope is sealed before the envelope-mount assembly is placed into the chamber so that the sealing and evacuation (or gas filling) operations are performed simultaneously.

United States Patent Boyce [54] SUBMINIATURE ELECTRIC LAMP HAVING ACOMPOSITE ENVELOPE Walter A. Boyce, Glen Ridge, NJ.

Westinghouse Electric Corporation, Pittsburgh, Pa.

22 Filed: Dec. 31, 1969 211 Appl.No.: 889,663

[72] Inventor: [73] Assignee:

[451 Jan. 18, 1972 Primary ExaminerDavid Schonberg AssistantExaminerPaul A. Sacher A!torneyA. T. Stratton, W. D. Palmer and D. S.Buleza [5 7] ABSTRACT The lamp, which may be of the incandescent orphotoflashtype, has an envelope composed of segments oflight-transmitting and infrared-radiation absorbing glass tubing thatare sealed together in abutting relationship. The infrared-radiationabsorbing end portion of the composite envelope is hermetically sealedto the lead wires and the seal is formed by focusing a beam of infraredradiation on the seal assembly. The envelope is evacuated, and filledwith gas if desired, through its opposite end which is then tipped off.Oxidation of the lead wires is reduced to a minimum by forming the sealinside a chamber that is evacuated, or filled with an inert gas, and haswalls which transmit infrared radiation. In the case of chamber sealing,the free end of the light-transmitting portion of the envelope is sealedbefore the envelope-mount assembly is placed into the chamber so thatthe sealing and evacuation (or gas filling) operations are performedsimultaneously.

5 Claims, 7 Drawing Figures PATENTEB JAN 1 8 I972 INVENTOR Walter A.Boyce AGENT WITNESSES W SUBMINIATURE ELECTRIC LAMP HAVING A COMPOSITEENVELOPE CROSS-REFERENCE TO RELATED APPLICATION The present invention isrelated to the subject matter disclosed in the commonly-assignedapplication Ser. No. 805,231 of W. L. Brundige filed Mar. 7, 1969, andentitled Method of Tipping Off the Exhaust Tube of an Electric Lamp, AndA Baseless Single-Ended Incandescent Lamp Produced By Such Method" (nowU.S. Pat. No. 3,551,725).

BACKGROUND OF THE INVENTION 1 Field of the Invention The presentinvention relates to electric lamps and has particular reference tosubminiature lamps of the incandescent or photoflash type and to animproved method for manufacturing such lamps.

2. Description of the Prior Art Electric lamps of extremely small sizeare well known in the art and are referred to as subminiature ormicrominiature lamps. Because of their small dimensions, such lamps aredifficult to manufacture and present quality control problems which arenot encountered in larger size lamps. A microminiature incandescent lamphaving an envelope that is sealed by a glass bead which is melted bypassing electric current through the filament and lamp leads during thesealing-in operation is disclosed in U.S. Pat. No. 3,275,879 issuedSept. 27, 1966, to P. C. Demarest et al. Another incandescent lamp ofthis type having a quartz envelope that is sealed by heating the quartzand press sealing it around the lead-in conductors is described in U.S.Pat. No. 3,462,209 issued Aug. 19, 1969, to E. G. Fridrich. Amicrominiature photoflash lamp having an envelope which is sealed by aglass bead which is fused to the mouth of the envelope by sharplydefined sealing fires is disclosed in U.S. Pat. No. 3,263,457, issuedAug. 2, I966, to H. Reiber.

While satisfactory lamps can be made using such techniques, they requireaccurately dimensioned interfitting envelopes and beads or the use ofgas sealing fires and pressing-sealing operations which are difficult tocontrol due to the extremely small size of the parts being joined.Unless adequate precautions are taken, the combustion products of thesealing fires will contaminate the finished lamps and excessiveoxidation of the metal parts of the lamps can easily occur which maycause leaky" seals.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly the generalobject of the present invention to provide an electric lamp of thesubminiature or microminiature type that can be readily and efficientlymanufactured without being contaminated.

Another object is the provision of a method of manufacturing such lampswithout the use of sealing fires, press-forming operations, oraccurately formed interfitting glass beads or the like that make itdifficult and time consuming to assemble the lamps and create conditionsduring the sealing-in'operation which could contaminate the lamp orbadly oxidize the lead wires or filament.

The foregoing objectives and other advantages are achieved in accordancewith the present invention by making the end segment of the envelopefrom infrared-absorbing glass and sealing it to the lead-in wires withinfrared radiation that is focused onto the seal assembly. In accordancewith one embodiment, the filament mount is sealed into one end of thecomposite envelope with infrared energy and the envelope is evacuatedthrough its opposite end which is then tipped off withconventionalsealing fires,

In another embodiment, oxidation of the lead wires during the sealing-inoperation is practically eliminated by placing the composite envelopeand filament mount in sealing relationship within an enclosure that hasinfrared-transmitting walls and is evacuated. The infrared energy sourceis located outside the' enclosure and the infrared radiation istransmitted through the walls of the enclosure and focused onto the endof the envelope to form the hermetic seal, thus completing the lamp. Thechamber can be filled with a suitable inert gas, such as nitrogen or thelike, to provide a gas-filled lamp if desired. Since the lamp isconcurrently evacuated (or gas filled) and sealed in accordance withthis embodiment, the opposite end of the envelope is sealed off when thecomposite envelope is formed. Preformed envelopes having flat or domedends can thus be used.

In either case, the envelope is sealed to the lead wires in a veryconvenient and efficient manner without the use of gassealing fires oraccurately dimensioned beads or the like.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be obtained by referring to the accompanying drawings, wherein:

FIG. 1 is an enlarged side elevational view of a subminiatureincandescent lamp embodying the present invention;

FIGS. 2(a) to 2(d) are elevational views illustrating the vari ousphases in the manufacture of the composite envelope employed in the lampshown in FIG. 1;

FIG. 3 is an elevational view, partly in section, illustrating theapparatus and procedure employed to seal the envelope t the lead wires;

FIG. 4 is a plan view of a preferred sealing apparatus wherein threeinfrared-generating incandescent lamps are equidistantly spaced aroundthe seal assembly to accelerate the sealing-in operation;

FIG. 5 is an elevational view of the sealed-in lamp prior to the exhaustand tipping-oi? operations;

FIG. 6 is an elevational view, partly in section, of another sealingapparatus which permits the seal to be effected in an evacuated orgas-filled chamber; and,

FIG. 7 is a plan view of a similar apparatus wherein three projectionlamps are used as exterior infrared-generating sources.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown asubminiature incandescent lamp 10 which embodies the present inventionand consists of a composite tubular envelope 11 having alight-transmitting body portion 12 that is terminated at one end by aprotruding seal tip 13 of fused glass and at its opposite end by a fusedbody 14 of infrared-absorbing glass. The glass body 14 is hermeticallysealed to a pair lead-in conductors 16, such as "dumet wires, that arefastened to an incandescible filament I7 and hold it within thelight-transmitting portion 12 of the envelope 11. The filament 17comprises a coil of suitable refractory wire such as tungsten that isconnected as by spot welding to the inner ends of the lead-in wires 16.The latter are preferably composed of dumet" wire and are of suchrigidity that the filament 17 is supported within the envelope l1 solelyby the lead-in wires. A glass stem or bead is accordingly not required.Dumet wire is well known in the art and consists of a nickel-iron corewire that is clad with copper and then heat treated to controllablyoxidize the copper surface. The core wire and copper cladding are bondedtogether metallurgically so that the composite wire has a continuousmetai structure. The core wire gives strength to the dumet" and itsexpansion as close to that of the soft glasses, such as lead glass,which are used in the envelopes of subminiature lamps of this type.

The term subminiature" as used herein and in the dependent claims refersto electric lamps having an overall length less than about 25millimeters and a maximum envelope diameter less than about 10millimeters and includes within its scope lamps ofvery small dimensionsthat are referred to in the art as microminiature lamps. The lamp 10shown in FIG. 1 had an overall length of approximately 10 millimetersand employed a TI envelope having an outside diameter of approximately 3millimeters.

As a specific example of suitable glasses, the light-transmittingportion 12 of the envelope 11 is composed of a sodalead glass well knownin the art. A typical formulation for such a glass is as follows: 62.7%Si 6.8% Na 0, 6.6% K 0, 21.8% Pb0, 1.7% R 0, and 0.4% incidentalimpurities (where R 0 is one or more additional alkali metal oxide suchas U0.)

The fused end segment 14 of the envelope I1 is composed of a suitableinfrared-absorbing glass that contains a small but sufficient amount ofiron oxide to render the glass infrared absorbing. Suchinfrared-absorbing glasses are also well known in the art and arecommercially available as Corning code 9362 and code 9363 sealingglasses. The glasses are greencolored potash-soda-lead glasses that haveviscosity and expansion characteristics that are almost identical withCorning code 0120 soda-lead glass so that the end segment 14 of theenvelope 11 can be readily sealed to the light-transmitting body portion12. The information published by Coming indicates that code 9362 andcode 9363 glasses have very high energy absorption in the infraredregion from approximately I to 4 microns wavelength and that code 9363glass has lower expansion characteristics which make it superior to code9362 glass for scaling to dumet" wire. Thus, an end segment 14 made ofeither of these glasses can be quickly heated and fused to the lead-inwires 16 by a focused beam of infrared radiation.

Transparent infrared-absorptive sealing glasses such as those disclosedin US. Pat. No. 3,445,256, issued May 20, 1969, which contain selectedamounts of PM, Si0 Fe 0 and alkali metal oxides can also be used.

MANUFACTURING METHOD AND APPARATUS The various operations in fabricatingthe composite envelope 11 are shown in FIGS. 2(a) to 2(d) and will nowbe described. As illustrated in FIG. 2(a), the envelope 1] includes asegment 12' of suitable soda-lead glass tubing and a shorter tubesegment 14' that is of the same diameter but composed ofinfrared-absorbing glass. One end of the soda-lead glass tubing 12' isheat softened and partially collapsed to fon'n a constriction 18, asshown in FIG. 2(b). The tube segments I2 and 14' are then placed inend-to-end abutting relationship and the opposite ends of the segmentsare temporarily closed off from the atmosphere by rubber caps 19 and 20or the like, as illustrated in FIG. 2(c). The abutting portions of thetube segments are then sealed together by a suitable gas fire (notshown), thus forming the composite envelope 11 shown in FIG. 2(d). Thesoftened abutting ends of the segments 12' and 14' are prevented fromcollapsing inwardly during the sealing operation by the air which istrapped within the tubes by the caps 19 and 20.

As shown in FIG. 3, the resulting composite envelope I1 is then placedover a filament mount that comprises the spaced lead-in wires 16 andjoined filament 17. The mount is held in upstanding position within theenvelope 11 by inserting the ends of the lead wires 16 into a head 22that has pockets 23 and 24 which nestingly accommodate the ends of thewires. The envelope 11 is maintained in sealing relationship with thefilament mount by a suitable holder 25 that grips'the upper end of theenvelope. The end segment 14 is then melted and collapsed down onto theunderlying portions of the lead-in wires 16 by energizing a suitableinfrared-energy source 26 and concentrating the infrared radiation intoa beam 31 that is focused onto the segment 14. In the embodiment shownin FIG. 3, the infrared-radiation source 26 comprises a 50 watt T12focus beam" projection lamp that has a coiled tungsten filament 28 andan internal reflector 30 which concentrates the infrared energy into afocused beam 31.

As shown in FIG. 4, three 500 watt focused beam" type projection lamps26, 32 and 33 are preferably used and are spaced approximately 120 apartaround the seal assembly so that the beams 31 of infrared energy arefocused onto the end segment I4 of the envelope II and rapidly anduniformly heat the glass to its melting temperature. With thisarrangement, an

henneticglass-to-metal seal was formed within approximately l 5 secondsin the case of the aforesaid Tl-type envelope. Any source of infraredenergy having means for focusing the radiations can be used. Thus, asuitable reflector and a halogentype infrared incandescent lamp ofsufficient wattage could be used in place of the aforementioned focusedbeam projection lamps.

The resulting sealed-in lamp 10' is then evacuated by connecting theopen end of the envelope II to a suitable exhaust system (not shown) andthe constriction 18 is tipped off with a sharply defined gas flame inthe usual manner, thus producing the finished lamp 10 shown in FIG. 1. Asuitableinert fill gas, such as nitrogen or the like at one or severalatmospheres pressure, can be introduced into theenvelope 11 after it hasbeen evacuated and before it is tipped off to provide a gasfilled lamp,if desired.

The present invention can also be employed to manufacture subminiaturephotoflash lamps. This can readily be accomplished by placing a suitableactinic fuel, such as a weighed amount of shredded zirconium, into theenvelope 11 near the constriction 18 before the envelope is placed overthe filament mount and sealed to the lead-in wires 16. In this case, thefilament 17 need not be coiled but can consist of a straight piece offine tungsten wire which preferably extends beyond the tips of the leadwires. A suitable ignition material or primer may be applied to thetungsten filament or to the tips of the lead wires 16 inaccordance withconventional photoflash lampmaking practice. Of course, the envelope 11in this case is also filled with oxygen at a suitable pressure such asI0 atmospheres and aprotective plastic coating is applied to theexterior surface of the envelope 11 to prevent it from shattering whenthe photoflash lamp is fired.

ALTERNATIVE EMBODIMENT In FIG. 6 there is shown an alternativeembodiment of the invention which enables a subminiature electric lampto be simultaneously sealed and evacuated, or filled with a suitableinert gas. This embodiment also enables preblown composite envelopes Ilato be used. As shown, the end of the light-transmitting tubular portion12a of such an envelope is sealed during the bulb-making operation byheating and molding it into a smooth dome l5.

As before, the filament mount is supported in upstanding position withinthe envelope He by a head 22a having a pair of pockets 23a and 24a whichnestingly receive the ends of the lead wires 16a. The domed compositeenvelope 11a is supported in enclosing and sealing relationship with thefilament mount by a bulb holder 34 that is adjustably fastened to asupport arm 35 anchored to the head 22a. The entire assembly isprotected from the atmosphere by an enclosure 36 that is composed of asuitable infrared-transmitting material, such as quartz or Vycor glass,and is hermetically joined to the peripheral edge of the head 22a. Theresulting airtight chamber is evacuated through a suitable conduit 38that extends through the head 22a and sealing of the infrared-absorbingglass portion 14a of the envelope 1 la is achieved by energizing anexterior source of infrared radiation, such as a focused beam"-typeprojection lamp 26, and directing the focused beam 31 of infraredradiation through the sidewall of the enclosure 36 onto the sealassembly.

Oxidation of the lead-in wires 16 during the sealing-in operation is, ofcourse, practically eliminated with this technique since the fusion ofthe envelope end segment I4a with the lead wires 16a is accomplished ina vacuum. If a gasfilled lamp 10a is desired, then the enclosure 36 isfilled with a suitable inert gas at the desired pressure after thechamber is evacuated and before the sealing-in operation is begun.

As will be noted in FIG. 7, equidistantly spaced sources of infraredenergy, such as three focused beam projection lamps 26, 32 and 33, arepreferably employed since this effects uniform heating of the glasssegment 14a and reduces the time required to complete the seal.

It will be appreciated from the aforesaid that the objects of theinvention have been achieved in that a very simple and practical methodand apparatus have been provided for manufacturing subminiature-typeelectric lamps. The glass-to-metal seal is achieved with infrared energyand permits lamps of very small size to be made without excessivelyoxidizing the lead-in wires or contaminating the lamp withgas-combustion products from sealing fires.

While several embodiments have been illustrated and described, it willbe understood that various modifications can be made in theconfiguration, arrangement, etc., of the lamp components and in themanufacturing process without departing from the spirit and scope of theinvention.

I claim as my invention:

1. A subminiature electric lamp comprising;

a composite envelope having a body portion of light-transmittingnoninfrared-absorptive glass that is terminated by an end segment offused glass that contains an amount of iron oxide sufficient to rendersaid end segment infrared absorptive,

an incandescible filament sealed within said envelope, and

a pair of spaced lead-in conductors connected to said filament andextending through said end segment of fused infrared-absorptive glass,

said lead-in conductors being embedded in and hermetically sealed tosaid end segment of fused infrared-absorptive glass and constituting thesole supporting means for said filament. 2. The subminiature electriclamp of claim 1 wherein; said filament comprises a refractory metalwire, the portions of said lead-in conductors that are embedded in saidend segment of fused infrared-absorptive glass comprise dumet wire, andg the light-transmitting body portion of said composite envelope iscomposed of soda-lead-type glass and the said fused end segment of theenvelope is composed of an infrared-absorptive glass selected from thegroup consisting of green-colored potash-soda-lead glass and atransparent glass that contains selected amounts of Pb0, Si0 Fe 0 and analkali metal oxide.

3. The subminiature electric lamp of claim 2 wherein;

said composite envelope also contains a shredded actinic fuel, anignition means and an oxygen atmosphere and the lamp thus comprises aphotoflash lamp, and said lead-in conductors comprise dumet wires.

4. The subminiature electric lamp of claim 2 wherein the end of saidenvelope opposite said end segment of fused infrared-absorptive glass isterminated by a protruding tip of fused glass.

5. The subminiature electric lamp of claim 2 wherein the end of saidenvelope opposite said end segment of fused infrared-absorptive glass issmooth and dome-shaped.

1. A subminiature electric lamp comprising; a composite envelope havinga body portion of light-transmitting noninfrared-absorptive glass thatis terminated by an end segment of fused glass that contains an amountof iron oxide sufficient to render said end segment infrared absorptive,an incandescible filament sealed within said envelope, and a pair ofspaced lead-in conductors connected to said filament and extendingthrough said end segment of fused infraredabsorptive glass, said lead-inconductors being embedded in and hermetically sealed to said end segmentof fused infrared-absorptive glass and constituting the sole supportingmeans for said filament.
 2. The subminiature electric lamp of claim 1wherein; said filament comprises a refractory metal wire, the portionsof said lead-in conductors that are embedded in said end segment offused infrared-absorptive glass comprise dumet wire, and thelight-transmitting body portion of said composite envelope is composedof soda-lead-type glass and the said fused end segment of the envelopeis composed of an infrared-absorptive glass selected from the groupconsisting of green-colored potash-soda-lead glass and a transparentglass that contains selected amounts of Pb0, Si02, Fe304 and an alkalimetal oxide.
 3. The subminiature electric lamp of claim 2 wherein; saidcomposite envelope also contains a shredded actinic fuel, an ignitionmeans and an oxygen atmosphere and the lamp thus comprises a photoflashlamp, and said lead-in conductors comprise dumet wires.
 4. Thesubminiature electric lamp of claim 2 wherein the end of said envelopeopposite said end segment of fused infrared-absorptive glass isterminated by a protruding tip of fused glass.
 5. The subminiatureelectric lamp of claim 2 wherein the end of said envelope opposite saidend segment of fused infrared-absorptive glass is smooth anddome-shaped.